Three commercial methods for serum ferritin compared and the high-dose "hook effect" eliminated.

We evaluated four commercial kits for measuring serum ferritin, based on three techniques: immunoradiometric assay, radioimmunoassay, and enzyme immunoassay. The kits evaluated were those manufactured by Abbott Laboratories, Clinical Assays, Corning Medical, and Ramco. Two of the immunoradiometric kits showed satisfactory results with respect to sensitivity and precision; they should be useful in diagnosing individuals with uncomplicated iron-deficiency anemia. One of the immunoradiometric assay kits, however, showed a high-dose "hook effect," beginning at 10 mg of ferritin per liter. We modified this kit to eliminate this effect, at least to ferritin concentrations of 33 mg/L. (We observed a ferritin value as high as 47 mg/L in one patient.) Results with all these kits did not inter-compare well for ferritin concentrations greater than 300 micrograms/L, a finding that casts further doubt on the controversial use of serum ferritin measurement in cases of iron overload.